1. Field of the Invention
The present invention relates generally to dry powder compositions and methods for their preparation and use. In particular, the present invention relates to methods for spray drying pharmaceutical and other compositions comprising a hydrophobic drug or other component and a hydrophilic excipient or other component.
2. Description of the Related Art
Over the years, certain drugs have been sold in formulations suitable for oral inhalation (pulmonary delivery) to treat various conditions in humans. Such pulmonary drug delivery formulations are designed to be inhaled by the patient so that the active drug within the dispersion reaches the lung. It has been found that certain drugs delivered to the lung are readily absorbed through the alveolar region directly into blood circulation. Such pulmonary delivery can be effective both for systemic delivery and for localized delivery to treat diseases of the lungs.
Pulmonary drug delivery can itself be achieved by different approaches, including liquid nebulizers, aerosol-based metered dose inhalers (MDI's), and dry powder dispersion devices. Aerosol-based MDI's are losing favor because they rely on the use of chlorofluorocarbons (CFC's), which are being banned because of their adverse effect on the ozone layer. Dry powder dispersion devices, which do not rely on CFC aerosol technology, are promising for delivering drugs that may be readily formulated as dry powders.
The ability to deliver pharmaceutical compositions as dry powders, however, is problematic in certain respects. The dosage of many pharmaceutical compositions is often critical, so it is desirable that dry powder delivery systems be able to accurately, precisely, and reliably deliver the intended amount of drug. Moreover, many pharmaceutical compositions are quite expensive. Thus, the ability to efficiently formulate, process, package, and deliver the dry powders with a minimal loss of drug is critical. With dry powder drug delivery, both the delivered dose efficiency, i.e. the percentage of drug from a unit dose receptacle which is aerosolized and delivered from a delivery device, and the median particle size distribution, i.e. the deviation from the median size, are critical to the successful delivery of powders to a patient's lungs.
A particularly promising approach for the pulmonary delivery of dry powder drugs utilizes a hand-held device with a hand pump for providing a source of pressurized gas. The pressurized gas is abruptly released through a powder dispersion device, such as a venturi nozzle, and the dispersed powder made available for patient inhalation. While advantageous in many respects, such hand-held devices are problematic in a number of other respects. The particles being delivered are usually less than 5 μm in size, making powder handling and dispersion more difficult than with larger particles. The problems are exacerbated by the relatively small volumes of pressurized gas, which are available using hand-actuated pumps. In particular, venturi dispersion devices are unsuitable for difficult-to-disperse powders when only small volumes of pressurized gas are available with the handpump. Another requirement for hand-held and other powder delivery devices is efficiency. High device efficiency in delivering the drug to the patient with the optimal size distribution for pulmonary delivery is essential for a commercially viable product.
Spray drying is a conventional chemical processing unit operation used to produce dry particulate solids from a variety of liquid and slurry starting materials. The use of spray drying for the formulation of dry powder pharmaceuticals is known, but has usually been limited to spray drying of hydrophilic drugs in aqueous solutions, usually in combination with hydrophilic excipients. Many drugs, however, are hydrophobic, preventing spray drying in aqueous solutions. While spray drying of hydrophobic materials can often be accomplished using an organic solvent, the use of such nonaqueous solvents generally limits the ability to simultaneously spray dry a hydrophilic excipient.
For these reasons, it would be desirable to provide improved methods for spray drying pharmaceutical and other compositions which comprise both hydrophobic and hydrophilic components, such as hydrophobic drugs and hydrophilic excipients. Such spray drying methods should be compatible with a wide variety of hydrophobic drugs as well as conventional hydrophilic excipients, such as povidone (polyvinylpyrrolidone) and other water soluble polymers, citric acid, mannitol, pectin and other water soluble carbohydrates, and particularly with those excipients which are accepted for use in inhalation formulations, such as lactose, sodium chloride, and sodium citrate. Such spray drying methods will preferably produce particles having a uniform size distribution, with a mean particle size below 10 μm, preferably below 5 μm, and a standard deviation less than or equal to ±2 μm. Such powders should further exhibit uniform composition from batch to batch so that any tendency for particles of different compositions and/or sizes to separate in the lungs will have a reproducible impact on the therapeutic effect. Additionally, such spray drying methods should provide for dry powders which are physically and chemically stable and which have low levels of any residual organic solvents or other components which might be used in the spray drying process. At least some of the above objectives will be met by the various embodiments of the present invention which are described in detail below.
Methods for spray drying hydrophobic and other drugs and components are described in U.S. Pat. Nos. 5,000,888; 5,026,550; 4,670,419; 4,540,602; and 4,486,435. Bloch and Speison (1983) Pharm. Acta Helv 58:14-22 teaches spray drying of hydrochlorothiazide and chlorthalidone (lipophilic drugs) and a hydrophilic adjuvant (pentaerythritol) in azeotropic solvents of dioxane-water and 2-ethoxyethanol-water. A number of Japanese Patent application Abstracts relate to spray drying of hydrophilic-hydrophobic product combinations, including JP 806766; JP 7242568; JP 7101884; JP 7101883; JP 71018982; JP 7101881; and JP 4036233. Other foreign patent publications relevant to spray drying hydrophilic-hydrophobic product combinations include FR 2594693; DE 2209477; and WO 88/07870.
WO 96/09814 describes spray dried pharmaceutical powders. In particular, Example 7 describes spray drying budesonide and lactose in ethanol where the budesonide is partially soluble and the lactose is insoluble. U.S. Pat. Nos. 5,260,306; 4,590,206; GB 2 105 189; and EP 072 046 describe a method for spray drying nedocromil sodium to form small particles preferably in the range from 2 to 15 μm for pulmonary delivery. U.S. Pat. No. 5,376,386, describes the preparation of particulate polysaccharide carriers for pulmonary drug delivery, where the carriers comprise particles sized from 5 to 1000 μm. Mumenthaler et al. (1994) Pharm. Res. 11:12 describes recombinant human growth hormone and recombinant tissue-type plasminogen activator. WO 95/23613 describes preparing an inhalation powder of DNase by spray drying using laboratory-scale equipment. WO 91/16882 describes a method for spray drying proteins and other drugs in liposome carriers.
The following applications assigned to the assignee of the present application each describe that spray drying may be used to prepare dry powders of biological macromolecules; U.S. Ser. No. 08/644,681, filed on May 8, 1996, which was a continuation-in-part of U.S. Ser. No. 08/423,515, filed on Apr. 14, 1995; U.S. Ser. No. 08/383,475, which was a continuation-in-part of U.S. Ser. No. 08/207,472, filed on Mar. 7, 1994; U.S. Ser. No. 08/472,563, filed on Apr. 14, 1995, which was a continuation-in-part of U.S. Ser. No. 08/417,507, filed on Apr. 4, 1995, now abandoned, which was a continuation of U.S. Ser. No. 08/044,358, filed on Apr. 7, 1993, now abandoned; U.S. Ser. No. 08/232,849, filed on Apr. 25, 1994, which was a continuation of U.S. Ser. No. 07/953,397, now abandoned. WO 94/07514 claims priority from U.S. Ser. No. 07/953,397. WO 95/24183 claims priority from U.S. Ser. Nos. 08/207,472 and 08/383,475.